Pressure suppression containment for a liquid-cooled nuclear reactor

ABSTRACT

Containment apparatus and a pressure suppression system for a liquid-cooled nuclear reactor. The apparatus includes a safety container formed by a spherical pressure shell and a condensation chamber filled with water arranged within the safety container. The condensation chamber, which is annular in shape, is bounded on the outside by the safety container, on the inside by a cylindrical wall within the container, and at the top and bottom by annular ends respectively connecting the top and the bottom of the cylinder with the safety container. A plurality of condensation tubes are provided to pass through the upper end and extend into the water in the condensation chamber. The reactor pressure vessel of the nuclear reactor is located within the cylindrical wall and surrounded by a cylindrical biological shield. The diameter of the shield is less than the diameter of the cylindrical wall so as to form an annular passageway between the shield and the cylindrical wall from the calotte-shaped region of the safety container above, to the calotte-shaped region of the safety container below, the condensation chamber.

United States Patent Ullrich et al.

[451 June6, 1972 [54] PRESSURE SUPPRESSION CONTAINMENT FOR A LIQUID-COOLED NUCLEAR REACTOR [72] Inventors: Walter Ullrich, Neu-Isenburg;Karl-Heinz Lohse, Frankfurt am Main; Jochen Leuteritz, Bruchkobel;Gunter Zeitzsche l, Frankfurt am Main; Robert Fassl, Munich, all ofGermany Licentia Patent-Verwaltungs-G.m.b.l Frankfurt am Main, GermanyOct. 9, 1968 [73] Assignee:

[22] Filed:

1 211 Appl. No.: 766,049

[52] U.S. Cl ..176/38, 176/54 5/1966 ll/l966 Bond, Jr. et a1.. ...l76/38X Webb ..l76/38 X FOREIGN PATENTS OR APPLICATIONS 1,303,680 8/l96lFrance 1 76/38 Primary Examiner-Leland A. Sebastian AssistantExaminer-S. R. Hellman AttorneySpencer & Kaye [57] ABSTRACT Containmentapparatus and a pressure suppression system for a liquid-cooled nuclearreactor. The apparatus includes a safety container formed by a sphericalpressure shell and a condensation chamber filled with water arrangedwithin the safety container. The condensation chamber, which is annularin shape, is bounded on the outside by the safety container, on theinside by a cylindrical wall within the container, and at the top andbottom by annular ends respectively connecting the top and the bottom ofthe cylinder with the safety container. A plurality of condensationtubes are provided to pass through the upper end and extend into thewater in the condensation chamber. The reactor pressure vessel of thenuclear reactor is located within the cylindrical wall and surrounded bya cylindrical biological shield. The diameter of the shield is less thanthe diameter of the cylindrical wall so as to form an annular passagewaybetween the shield and the cylindrical wall from the calotte-shapedregion of the safety container above, to the calotte-shaped region ofthe safety container below, the condensation chamber.

16 Claims, 5 Drawing Figures PATENTEDJUH 6 I972 3.6681369 SHEET 1 or 3INVENTORS WALTER ULLRICH, KARL-HEINZ LOHSE, JO CHEN LEUTERITZ, GUNTERZEITZSCHEL, ROBERT FASSL BY z ATTORNEYQS PATENTEDJUH 6 I972 3 668 O69SHEET 2 OF 3 Fly. 2::

7 INVENTORS WALTER ULLRICH, KARL-HEINZ LOHSE, CHEN LEUTERITZ,

GUNTER ZEITZSCHEL ROBERT FASSL BY M I ATTORNEYS PATENTEDJUH 6 I972 3.668 O69 sum 3 or 3 INVENTORS WALTER ULLRICH, KARL- HEINZ LOHSE,

JOCHEN LEUTERITZ, GUNTER ZEITZSCHEL.

ROBERT FASSL 8v M 5 Kaye A TTORNE V5 BACKGROUND OF THE INVENTION Thepresent invention relates to containment and pressure suppressionapparatus for a liquid-cooled nuclear reactor.

The primary system of most types of nuclear reactors used in nuclearpower plants is conventionally enclosed in a gastight safety containerformed by a spherical or otherwise suitably shaped pressure shell madeof steel or concrete. This arrangement is known as containment."

The primary function of the safety container is to continuallycontrol'the radioactive material which is liberated during normaloperation of the nuclear reactor; that is, to contain the radioactivematerial that leaks out so that it can be safely disposed of. The safetycontainer also serves the function, in the case of a major reactoraccident, to contain the escaping material until its activity haddecayed or it has been eliminated. This requires that the safetycontainer be constructed to withstand the thermal and pressure stresseswhich may arise under the severest accident conditions. In the case ofwater-cooled nuclear reactors these stresses are primarily due to theliberated steam.

The first safety containers which were constructed for water-cooledreactors were dimensioned so that they could withstand the pressurewhich would arise if the entire primary circulation were allowed toescape. It was later discovered, however, that the safety containercould be made much smaller and much safer if a pressure suppressionsystem were provided. In a system such as this, thesteam-water-air-mixture which is produced during an accident is pipedvia tubes into a ready water reservoir where the steam is condensed. Asa result, only a portion of the water in the primary circulation systemcontributes to an increase in pressure.

It may be easily seen that both the overall size and the wall thicknessof a safety container used with a pressure suppression system canadvantageously be reduced. In fact, a pressure suppression system alsobrings with it a number of ancillary advantages which increase thesafety of the nuclear reactor.

For example, the overpressure which is generated during an accident isquickly reduced, and by far the major portion of the active material isheld back in the condensation water.

In practice, a pressure suppression system is constructed by arrangingcondensation or suppression" chambers within the safety container. Theparticular configuration of pressure suppression containment has beenthe subject of considerable research. See, for example, Ashworth et al.,Pressure Suppression," Nuclear Engineering 5 (1962), pp. 313-321;Welchel, Pressure Suppression Approved for Humboldt Bay," ElectricalWorld, Nov., 1960, pp. 68-72, 98; Welchel and Robbins, PressureSuppression Containment for Nuclear Power Plants," ASME, Paper No. 59-A-2l5, Oct., 1960, pp. l-lO; and U.S. Pat.No. 3,115,450 to Schanz (FIG.7).

Although the prior art knows a number of variations of pressuresuppression and containment apparatus, the known types of constructionare all based upon the following principle: The reactor pressure vessel,together with its surrounding biological shield, is arranged inside acompletely enclosed, dry wall protective chamber. The protective chamberis surrounded, in turn, by the condensation (suppression) chamber. Ventpipes are provided to communicate between the reactor pressure vesseland the condensation chamber. The protective chamber, as well as thecondensation chamber, are then encapsulated by the outer pressure shellor safety container.

This type of construction has a number of disadvantages. In every case,a portion of the main steam conduit which leads from the reactor throughthe safety container to the turbine will be located between theprotective chamber and the pressure shell. If this portion of the steamconduit breaks, it can force water from the condensation chamber throughthe condensation tubes into the protective chamber; that is, exactly theopposite of what is desired. In addition, the space into which the steamflows in case of an accident hereinafter referred to as the pressurechamber" will be relatively small. This fact can result in the exertionof unfavorable loads or pressures against the wall of the safetycontainer.

SUMMARY OF THE INVENTION It is, therefore, a primary object of thepresent invention to provide containment apparatus having a safetycontainer in the favorable shape of a sphere and a pressure reducing orpressure suppression system which overcomes the disadvantages of theprior art systems described above.

It is an additional object of the present invention to providecontainment and pressure suppression apparatus which directs steam to acondensation chamber regardless where a break occurs, in the primarycirculation system, within the safety container.

It is an additional object of the present invention to providecontainment and pressure suppression apparatus which includes sufficientcompressable medium, such as air, for the initial expansion of steam inthe case of an accident.

A further object of the present invention is to provide a liquid-coolednuclear reactor with a compact, gas-tight safety container which can bebuilt at a reduced cost.

A still further object of the present invention is to construct aliquid-cooled nuclear reactor within a spherical safety container sothat optimum use will be made of the available space in accommodatingthe necessary accessories.

These, as well as other objects which will become apparent in thediscussion that follows, are achieved, according to the presentinvention, by constructing the containment and pressure suppressionapparatus of a liquid-cooled nuclear reactor in the following manner:

An annular condensation chamber filled with water, is arranged within asafety container formed by a spherical pressure shell. The condensationchamber is bounded at the outside by the spherical shell, on the insideby a cylindrical wall arranged within the spherical shell, and at thetop and bottom by annular shaped ends connecting, respectively, the topand bottom of the cylindrical wall with the spherical shell. The heightof the cylindrical wall is made somewhat less than the diameter of thesafety container so that calotte-shaped spaces within the safetycontainer will remain both above and below the condensation chamber.Condensation tubes, projecting from the upper annular end into thecondensation chamber, place the upper calotte-shaped space incommunication with the water in the chamber. A cylindrical biologicalshield, the diameter of which is somewhat less than the diameter of thecylindrical wall, is arranged coaxially within the cylindrical wall andforms an annular passageway therewith from the upper to the lowercalotte-shaped space. The reactor pressure vessel is then located withinthe biological shield.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalview of the pressure suppression and containment apparatus according tothe present invention.

FIGS. 2a and 2b are two quarter sections of the pressure suppression andcontainment apparatus of FIG. 1 taken along the lines 2a and 2b,respectively.

FIG. 3 is a simplified representation of the apparatus of FIG. 1.

FIG. 4 is a sectional view of a detail of the apparatus of FIG. 1showing the manner in which the condensation tubes are attached to theupper annular end.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,FIG. I shows, in detail, a longitudinal section of the spherical safetycontainer according to the present invention. Since FIG. 3 is asimplified illustration of that which is shown in FIG. 1, FIG. 3 will bedescribed together with FIG. 1.

The safety container consists of a steel sphere 5 and an outer sealingskin 6, the sphere 5 and skin 6 being connected to each other by way ofsuitable spacers or indentations. The space between the sphere and theskin is kept at a reduced pressure, by a vacuum pump or other suitablemeans. The steel sphere rests on a foundation in the building housingthe reactor.

The actual reactor, namely, the reactor pressure vessel for awater-cooled reactor with the reactor core and the like, is arranged atthe center of the sphere. Various embodiments of such reactors are wellknown in the art so they will not be described here in detail. All thatis shown are the control rod drives 14, the coolant circulating pumps16, as well as the primary steam conduit 24 which passes through thepressure shell.

The pressure vessel 19 is surrounded axially by a concrete jacket,constituting the biological shield 20, and rests on a socket thereof atits lower end. The pressure suppression system lies concentrically withrespect to the shield; it takes the form of an annular condensationchamber 8 which is bounded on the outside by the wall of the sphere, onthe inside by a steel cylinder 8a, and at the top and on the bottom byannular steel ends 8b, 8c. As shown in the drawings, the upper steel end8b and the lower steel end 80 may assume the shape of sections of atoroid. The condensation chamber is half filled with water 10, therebeing a large number of condensation tubes 7 which extend from the upperannular end to a point below the water level. In the case of a 600 MWpower plant, there may, for example, be 76 such tubes, each having adiameter of 61 cm. These tubes provide a permanently open communicationbetween the condensation water and the remaining volume or free volume"of the pressure chamber. The walls within the safety container are sofashioned that the spaces formed between them have a large free crosssection; they therefore form spaces within the pressure chamber throughwhich gases may flow, practically unhindered, to quickly establish apressure equilibrium.

As best seen in FIG. 3, the pressure chamber so produced has a verylarge volume. It consists, for all practical purposes, of the twocalotte-shaped spaces above and below the condensation chamber, and theinner cylinder, between the biological shield and the condensationchamber, which communicates between them. If the primary circulationsystem ruptures, the very large volume will itself already contribute toa reduction in pressure. Furthermore, the steam-air-water-mixture in thepressure chamber will be piped through the condensation tubes into thecold water, where it will condense and keep the pressure rise withinreasonable limits.

The bottom of the sphere is provided with a cylindrical extension;namely, the bottom trough 23, which is needed to complete the drive forthe control rods. The presence of this bottom trough permits the sphereto be made smaller than otherwise, this reduction in size providing theadvantages of thinner walls, lower weights, and lower price. The bottomtrough 23 is provided with an access lock 22 having an inclined axis.The purpose of the inclined axis is to obtain a spherical opening in theextension 23. Two vertical doors are provided within the lock. Thisconstruction makes it possible to build and test the body of the lockseparately and then to weld it on after the safety container has beenpressure-tested. A cover is provided on the inside of the container,instead of the missing look, while the container is being tested.

The annular steel ends 8b, 80 have the advantage, over the other typesof closures, that they have a very small radius.

The annular ends can be produced, for example, by forming a steel tubeinto the shape of a ring, to produce an annulus, and cutting ithorizontally, along the desired plane, so that the small radius of thetube will be taken into account. In this way, it is possible to keep thewall thickness of the annular ends below the mm annealing limit whichmust be observed during welding operations.

A shown in FIGS. 2 and 4, pressure struts 25 are attached to the annularends. The pulling forces which arise when the ends are subjected topressure would normally have a marked influence on the spherical shell;the pressure struts pick up these forces, however, so that it ispossible to make do without the sphere thicknesses which would otherwisebe necessary to provide reinforcement. As shown in FIG. 4, the pressurestruts and the annular ends are attached to the sphere 5, and the innersteel cylinder 8a, by way of a. member 28 having a K- shaped crosssection.

It should also be noted that the vertical condensation tubes arestraight and are provided at the top with inlet funnels. These tubesthus exhibit a significantly lower pressure drop when fluid flowsthrough, than do the bent condensation tubes of the prior art. The lowpressure drop allows the pressure differential between the pressurechamber and the condensation chamber to be kept small, so that wallthicknesses and construction costs can be reduced.

For reasons of safety, the condensation tubes are mutually braced eachagainst the other by a bracket 26. This is advisable because, due tocondensation shocks and other thermo-hydraulic functions, transverseforces may arise at the lower ends of the tubes. Without this bracing,the relatively long condensation tubes, which are welded into the upperend plate, would have to be made substantially thicker with acorresponding increase in cost. The mutual bracing also permits thecondensation tubes to be combined into a packet or unit, so that notransverse forces are transmitted to the inner cylinder 8a or to thespherical shell 5.

The above described bracing or anchoring of the condensation tubes canalso be used to provide the base for a circular cat walk 9 forinspection of the reactor. Furthermore, the anchoring makes it possibleto provide bafile plates 27, the purpose of which is to preventcirculation of the water, to eliminate the necessity of welded on pieceswhich would impede the expansion of the containment shells.

In all the containment systems heretofore known, the steel shell couldbe damaged if a valve spindle or any other circulation system part isblown off and flung against it under the pressure prevailing in theconduits. By providing protective plates near openings and an internalconcrete cover 4 on the pressure shell and on the inner cylinder 8a ofthe condensation chamber 8, the parts of the container'which are underpressure are safely protected. This protective concrete must leave freelarge cross sections above the upper end plate 8b so as to allow for afluid flow out of the pressure chamber into the condensation tubes. Thisis done by means of profiled concrete beams which fully overlap oneanother but which leave free large openings that pemiit the flow offluid.

The safety containerhas covers 1 and 2 for charging the reactor and forpermitting assembly and installation of parts. During operation of thereactor these covers are screwed to the sphere, with the aid of conicalseating surfaces, to form a gas-tight seal.

Positioning the axial pumps, which circulate the coolant, within theinterior of the safety container and directly on the pressure vessel hasadvantage, compared to external pump circulating systems that thepressure suppression system can be made still smaller. One reason forthis is that less space is needed; another reason is that there is asmaller volume of water in the primary circulation system which requiresless water in the condensation chamber. Another favorable result is thatthe largest possible rupture opening under the worst possible accidentconditions will be smaller.

The safety container according to the present invention may be used toparticular advantage with boiling water reactors. It can also be used,however, with pressure water reactors or any other reactors employed inthe chemical engineering arts.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations.

We claim:

1. Containment and pressure suppression apparatus for a liquid-coolednuclear reactor comprising, in combination:

a. a spherical pressure shell constituting a safety container;

b. a cylinder arranged within said shell, the axis of said cylinderbeing vertical and passing through the center of said shell, and theheight of said cylinder being less than the diameter of said shell;

0. an upper annular end connecting the top of said cylinder with saidshell;

d. a lower annular end connecting the bottom of said cylinder with saidshell; said shell, said cylinder and said upper and lower endsconstituting the walls of a condensation chamber and leavingcalotte-shaped regions of said shell above and below said condensationchamber;

e. tube means projecting from said upper end into the condensationchamber for placing the calotte-shaped region above the condensationchamber in communication with a condensation coolant in saidcondensation chamber;

f. a cylindrical biological shield arranged coaxially within saidcylinder, thereby forming an annular passageway between said shield andsaid cylinder from the calotteshaped region above to the calotte-shapedregion below the condensation chamber;

g. a reactor pressure vessel arranged within said shield; and

h. a steam pipe arranged in said calotte-shaped region above thecondensation chamber for passing steam from said reactor pressure vesselout of said shell.

2. The apparatus defined in claim 1 wherein the upper and lower annularends have the shape of sections of a toroid.

3. The apparatus defined in claim 2, further comprising a pressure stripmeans for reinforcing said upper and lower annular ends.

4. The apparatus defined in claim 3, wherein said pressure strip meanshas a plurality of pressure struts connected to said shell and to saidcylinder, and further including members each having a K-shaped crosssection and connected to respective ones of said pressure struts, saidshell, and a respective one of said upper and lower annular ends.

5. The apparatus defined in claim 4, further comprising a cylindricalextension projecting downward from said shell beneath said reactorpressure vessel.

6. The apparatus defined in claim 5, further comprising an access lockhaving at least two vertical lock doors, said access lock being attachedto said cylindrical extension.

7. The apparatus defined in claim 5 wherein said tube means include aplurality of vertically arranged straight tubes, the upper ends of whichare provided with outwardly flaring funnels and welded to said upperannular end.

8. The apparatus defined in claim 7 wherein the lower ends of said tubesare connected together by a brace.

9. The apparatus defined in claim 8, further comprising access walkmeans arranged within said condensation chamber and supported by saidbrace, for permitting inspection of the nuclear reactor.

10. The apparatus defined in claim 9, further comprising bafile platemeans, attached to said brace, for preventing circulation of the waterin the condensation chamber. 7

11. The apparatus defined in claim 10 wherein portions of said cylinderand said shell are provided with concrete cover means to preventpunctures in the regions of said cylinder and said shell which aresubjected to pressure.

12. The apparatus defined in claim 11, further comprising pump means,arranged within said shell at said reactor pressure vessel, forcirculating the reactor coolant.

13. The apparatus defined in claim 12 wherein said shell includes asteel wall surrounded by a sealing layer, said sealing layer beingseparated from said steel wall by spacing means, the space between saidsteel wall and said sealing layer being maintained at a reducedpressure.

14. The apparatus defined in claim 13 wherein said upper and lowerannular ends are made of steel.

15. The apparatus defined in claim 14 wherein said shell is made ofconcrete.

16. The apparatus defined in claim 14 wherein said shell is made ofsteel.

2. The apparatus defined in claim 1 wherein the upper and lower annularends have the shape of sections of a toroid.
 3. The apparatus defined inclaim 2, further comprising a pressure strip means for reinforcing saidUpper and lower annular ends.
 4. The apparatus defined in claim 3,wherein said pressure strip means has a plurality of pressure strutsconnected to said shell and to said cylinder, and further includingmembers each having a K-shaped cross section and connected to respectiveones of said pressure struts, said shell, and a respective one of saidupper and lower annular ends.
 5. The apparatus defined in claim 4,further comprising a cylindrical extension projecting downward from saidshell beneath said reactor pressure vessel.
 6. The apparatus defined inclaim 5, further comprising an access lock having at least two verticallock doors, said access lock being attached to said cylindricalextension.
 7. The apparatus defined in claim 5 wherein said tube meansinclude a plurality of vertically arranged straight tubes, the upperends of which are provided with outwardly flaring funnels and welded tosaid upper annular end.
 8. The apparatus defined in claim 7 wherein thelower ends of said tubes are connected together by a brace.
 9. Theapparatus defined in claim 8, further comprising access walk meansarranged within said condensation chamber and supported by said brace,for permitting inspection of the nuclear reactor.
 10. The apparatusdefined in claim 9, further comprising baffle plate means, attached tosaid brace, for preventing circulation of the water in the condensationchamber.
 11. The apparatus defined in claim 10 wherein portions of saidcylinder and said shell are provided with concrete cover means toprevent punctures in the regions of said cylinder and said shell whichare subjected to pressure.
 12. The apparatus defined in claim 11,further comprising pump means, arranged within said shell at saidreactor pressure vessel, for circulating the reactor coolant.
 13. Theapparatus defined in claim 12 wherein said shell includes a steel wallsurrounded by a sealing layer, said sealing layer being separated fromsaid steel wall by spacing means, the space between said steel wall andsaid sealing layer being maintained at a reduced pressure.
 14. Theapparatus defined in claim 13 wherein said upper and lower annular endsare made of steel.
 15. The apparatus defined in claim 14 wherein saidshell is made of concrete.
 16. The apparatus defined in claim 14 whereinsaid shell is made of steel.